The causes of stuttering are not fully understood but researchers believe that it may be caused by interference between the left and right hemispheres of the brain competing against one another to send signals to the muscles used to produce speech. These conflicting signals ultimately impair the muscles resulting in stuttering, which is typically characterized by interruptions in speech flow, repetitions, prolongations, and pauses in speech.
The treatments for stuttering are varied and include methods such as psychological therapy, drug, therapy, and altered auditory feedback (AAF). Most AAF treatments can be divided into three categories: delayed auditory feedback (DAF), frequency-shifted auditor, feedback (FAF), and masked auditory feedback (MAF). Treatment using DAF typically utilizes a user's own voice which is delayed between 50 to 200 ms and then relayed back to the user, usually through headphones or an earpiece. This type of treatment relies on the “choral effect”, which occurs when people who stutter speak or sing in unison with others, experience a dramatic reduction or even elimination of stuttering.
Treatments using FAF are based on changing the frequency characteristics of the user's voice by, about a half octave such that the relayed auditory feedback sounds somewhat distorted to the speaker. This frequency shift is believed to effect the user's brain in the same manner as DAF treatment. The MAF treatment involves generating a synthetic sine signal corresponding to the user's own phonetic frequency and relaying this masking feedback to the user.
These treatments usually involve placing a device within the ear canal of the user to completely or partially obstruct the opening much like air-conduction hearing aids. However, such devices are intended to be left in place even when the user is not talking and will also obstruct ambient noises that the user may wish to hear. Moreover, such in-ear devices (as well as other external devices) are usually visible to others and may thus be a deterrent for use by some users for aesthetic reasons. Other devices utilizing such treatments are placed upon a post which is permanently implanted into the skull of the user. However, such devices require invasive surgery and present various complications which may occur as a result.
Accordingly, there exists a need for methods and apparatus for receiving and processing a user's voice and effectively transmitting these processed signals back to the user with minimal obstruction.